Analog Modulation AM(Amplitude Modulation) Demodulation of AM Signals Angle Modulation
Analog Modulation AM(Amplitude Modulation) Demodulation of AM Signals Angle Modulation
Why modulate Ease of radiation ■The size of antenna oc入l4=cl4f If we wish to throw a piece of paper(baseband signal),it cannot go too far by itself.But by wrapping it around a stone(carrier),it can be thrown over a longer distance Simultaneous transmission of several signals FDM(Frequency Division Modulation) Reduce the influence of interference ·Frequency Hopping Effecting the exchange of SNR with B Shannon's equation:C=Blog,(1+SNR) C is rate of information change per second(bit/s)
Why modulate ? ◼ Ease of radiation ◼ The size of antenna /4 = c/4f ◼ If we wish to throw a piece of paper(baseband signal), it cannot go too far by itself. But by wrapping it around a stone(carrier), it can be thrown over a longer distance ◼ Simultaneous transmission of several signals ◼ FDM(Frequency Division Modulation) ◼ Reduce the influence of interference ◼ Frequency Hopping ◼ Effecting the exchange of SNR with B ◼ Shannon’s equation : ◼ C is rate of information change per second (bit/s) 2 C B SNR = + log (1 )
Properties of analog modulation ■ Time domain representation of the modulated signal Frequency domain representation of the modulated signal Bandwidth of the modulated signal Power component of the modulated signal SNR after demodulation Message Modulated ■ Modulator Signal Signal (or modulating Signal)
Properties of analog modulation ◼ Time domain representation of the modulated signal ◼ Frequency domain representation of the modulated signal ◼ Bandwidth of the modulated signal ◼ Power component of the modulated signal ◼ SNR after demodulation ◼ Modulator Message Signal (or modulating Signal) Modulated Signal
AM (Amplitude modulation) Also known as "Linear modulation) Small bandwidth,Power inefficient ■Applications AM radio,TV video broadcasting(VSB),Point-to-point communications(SSB),Transmission of many telephone channels over microwave links ■ Class of AM DSB-AM(Double Side Band-AM) BW=2W=2*BW of the message signal SSB-AM(Single Side Band-AM) BW=W VSB-AM(Vestigial Side Band-AM) ■BW=W~2W
AM (Amplitude modulation) ◼ Also known as “Linear modulation) ◼ Small bandwidth, Power inefficient ◼ Applications ◼ AM radio, TV video broadcasting(VSB), Point-to-point communications(SSB), Transmission of many telephone channels over microwave links ◼ Class of AM ◼ DSB-AM(Double Side Band – AM) ◼ BW = 2W = 2 * BW of the message signal ◼ SSB-AM(Single Side Band – AM) ◼ BW = W ◼ VSB-AM(Vestigial Side Band – AM) ◼ BW = W ~ 2W
DSB-AM Amplitude of modulated signal is proportional to the message signal m(t)_ (t)=Am(t)cos(2πft) c(t)=A.cos(2πft) m(t) m(t)cos wr m() -m(t)
DSB – AM ◼ Amplitude of modulated signal is proportional to the message signal ( ) cos(2 ) c c c t A f t = ( ) ( )cos(2 ) m t( ) u t A m t f t = c c